Preparation of alkyl ammonium nitrates



United States Patent 3,225,050 PREPARATION OF ALKYL AMMONIUM NITRATES Gerhard Barth-Wehrenalp, Ambler, Robert A. Bernoit, Lynnewood Gardens, Elkins Park, and David M. Gardner, North Wales, Pa., assignors to Pennsalt Chemicals Corporation, Philadelphia, Pa., a corporation of Pennsylvania N0 Drawing. Filed May 18, 1960, Ser. No. 29,794

19 Claims. (Cl. 260-268) This invention relates to a novel process for making alkyl ammonium nitrates, preferably quaternary ammonium nitrates. In particular, this invention relates to an improved process for preparing high purity alkyl ammonium nitrates by reaction of dinitrogen tetroxide (N 0 with alkyl ammonium halide.

Alkyl ammonium nitrates and particularly quaternary ammonium nitrates are important chemical compounds useful as fertilizers, disinfectants and more recently as rocket propellants. In the latter application it is imperative that the compounds be of high purity and be free of alkali metal and chlorine atoms because such contaminants seriously affect the efiiciency of the propellant by lowering specific impulse and by affecting its thermal and shock sensitivity.

It is known in the literature (Addison et al., J. Chem. 800., pp. 1298 (1951)) to react liquid N 0 at low temperatures with organic ammonium halides and obtain the corresponding nitrate. However, when this prior art process is carried out, a number of side reactions occur. For example, the addition of N 0,, to an organic ammonium chloride yields nitrosoamine which contaminates the ammonium nitrate product. Likewise, with quaternary ammonium chlorides the literature concludes that more than a single reaction occurs with N 0 This is confirmed by experiments which show the formation of color d impure products on reaction of N 0 with quaternary ammonium chlorides. Side reactions giving such unwanted by-products are to be expected when using N 0 with organic compounds because of the tendency of N 0 to effect nitration and/or oxidation of organic radicals.

It has now unexpectedly been found that conversion of alkyl ammonium halides to nitrates can be effected smoothing, without undesirable side reactions to yield the nitrates in essentially quantitative conversion and in very high purity free of halides and alkali metals. This result is achieved by the novel process of this invention which comprises reacting N 0 with an alkyl ammonium halide (e.g. fluorides, chlorides, and bromides), said reaction being conducted in a liquid having at least partial solubility for the alkyl ammonium nitrate, venting the volatile by-products formed during the reaction and separating from the reaction mass the pure halide-free alkyl ammonium nitrate which is formed. Thc reaction is illustrated by the following equation:

results in a product free of by-product contaminations 3,225,050 Patented Dec. 21, 1965 When a quaternary ammonium chloride or fluoride is used the sole volatile by-product will be the corresponding nitrosyl halide. However, when a quanternary ammonium bromide is employed there will be formed as by-products some nitrosyl bromide, nitric oxide and bromine. All of these by-products are volatile, however, and are readily vented from the reaction mass. There is the further advantage of this process that the nitrosyl halide formed may be recovered and converted to N 0 by heating it in the presence of oxygen (e.g. air). As indicated, reaction at ambient pressure is preferred, but operation above or below atmospheric pressure is possible as is operation at low and elevated temperatures. Where the reactant and product nitrate are both very soluble in the reaction solvent, the product is isolated easily by adding a non-solvent for the product and precipitating it out of solution. The solid precipitate is then simply filtered off and washed with a highly volatile solvent (e.g. acetone) to remove any adhering solvent. If the adhering solvent is itself highly volatile, the washing step may be eliminated. In a preferred technique, however, the solvent system will be chosen so that both the quaternary ammonium halide and its nitrate product have only partial solubility in the solvent. In this technique the product nitrate quickly saturates the solvent and precipitates from the solution as it is formed. When the reaction is completed the product is simply filtered off, washed if necessary to remove adhering solvent, and dried. This proceudre has another important advantage in that the filtrate which is already saturated with the nitrate product is ready for reuse. Upon addition of more quaternary ammonium halide and N 0 the process continues and this cyclis process may be repeated indefinitely.

The solvent selected for use in this process will generally be a polar solvent, but as will be seen later, the liquid reaction medium may consist of mixtures in which one or more components are non-solvent for the quaternary ammonium reactant or product. The optimum solvent or solvent system will frequently depend upon the particular quaternary ammonium halide used, but as-will be seen, an optimum liquid reaction medium can be determined with no difficulty. Preferably, the classes of solvents used will include acids, particularly lower aliphatic acids (e.g. formic, acetic, propionic, etc.), liquid nitriles (e.g. acetonitrile, propionitrile, etc.), liquid amides such as N.N-di-lower alkyl substituted amides of lower aliphatic acids (e.g. dimethylformamide, diethylformamide, dimethylacetamide), liquid nitrated lower alkanes such as nitromethane, etc., and liquid sulfoxides such as dimethyl sulfoxide. Also, quite useful, but less preferred solvents include water and the lower aliphatic alcohols (e.g., methanol, ethanol, butanol, amyl alcohol and the like).

Determination of an optimum solvent or solvent system is 'done quite easily with simple experiments. A few crystals (about 0.1 g.) of the desired reactant chloride and product nitrate are added to about g. samples of various proposed solvents and visual observation made. The chloride preferably should show some solubility. If in doubt, an aliquot sample may be evaporated to deter mine if a residue is obtained, thus showing solubility. Likewise with the nitrate, partial solubility may be determined. If the nitrate is highly or completely soluble an optimum solvent system is obtained by the addition of a miscible liquid having little or no solvent properties for the quaternary ammonium nitrate. The amount to add is determined by observing how much is required to cause precipitation of the nitrate in the test sample. Preferably, the solubility of the nitrate in the liquid reaction medium will be between about 0.1% and 1% by weight.

It will be understood that because they are both ionic, the halide and nitrate will generally have about the same order of solubility. However, nitrates are usually somewhat more soluble than halides and it is possible that the halide will be insoluble and the nitrate partially soluble in the raction medium. In such a case the reaction will proceed readily because the nitrate formed on the insoluble halide particle will be dissolved away and fresh halide surface will be exposed. If, however, the halide is insoluble and the nitrate is completely insoluble or less soluble than about 0.1%, the reaction occurs on the surface of the reacting halide particles and prevents further reaction. Thus, some solubility of the nitrate is required to permit exposure of fresh reacting surface. When carrying out the process with quaternary ammonium halides which are insoluble in the reaction medium it is desirable that the halide reactant be powdered or finely divided to expose large surface area and enhance reaction.

When employing the technique of adjusting the solubility, the preferred non-solvent liquids are the wellknown class of halocarbons and preferably the chlorofluorocarbons. Examples of useful liquids for adjusting nitrate solubility are carbon tetrachloride, chloroform, dichloromethane, 1,1,1-trichloroethane, 1,1 dichloroethane, pentachloroethane, fluoropentachloroethane, perch-loroethane, 1,1,2 trifluoro trichloroethane, 1,2 difluorotetrachlorethane, 1,1 difluorotetrachlorethane, fiuorotrichloromethane, 1,1,1-trifluoro trichloroethane, 1,2-dibromotetrafluoroethane, and the like. Other liquids inert to the reactants and products and having little or no solubility for the quaternary ammonium nitrate product may also be used.

As indicated, the components of the liquid system will be essentially unreactive to the alkyl ammonium halide and N teactants as well as the nitrate and nitrosyl halide products. Although certain solvents such as alcohols do slowly react with N 0 these solvents may be used because the ionic reaction of this process is so fast that it precludes reaction between the solvent and N 0 However, where the solubility of the reactants is rather low the possibility of such reaction with the solvent does exist and therefore these compounds are not preferred. The preferred liquid system will be comprised of acetic acid and trichlorotrifluoroethane and these liquids will be used in approximately equivolume amounts.

The quaternary ammonium halide reactants are well known compounds and may be selected from any of the wide variety existing. When using this process to prepare high energy fuels, the quaternary ammonium compound selected will usually be a rather compact molecule, as for example the tetra-lower alkyl ammonium halides, the quaternary ammonium salts of polyamines (e.g. diamines, triamines, etc.), the quaternary ammonium salts of polyalkylenepolyamines (e.g. those quaternaries from triethylenediamine) and the like. Examples of such quaternary salts include those obtained by quaternizing trimethylamine, dimethylethylamine, tri-isopropylamine, tri-butylamine, triethylamine, triamylamine, N,N,N,N'-tetramethylethylenediamine, N,N' dimethyldiethylenediamine, triethylenediamine, and diethylene methylethylenediamine with an alkyl halide such as methylbromide and ethyl chloride. In lieu of the alkyl and alkylene amine derived quaternary compounds, others may also be used, as for example those obtained by the action of benzyl chloride on other tertiary aromatic and heterocyclic amines such as pyridine and its derivatives, N-alkyl piperidines, N,N-dimethylaniline, diphenylmethylamine and the like. Some specific quaternary ammonium compounds of particular value as intermediates to nitrate salts for rocket fuels are trimethylisopropylammonium chloride, trimethyl ethylammonium chloride, dimethyldiethylammonium chloride, dimethyltert-butyl-ethylammonium chloride, triethylisopropylammonium chloride, N,N-tetramethyl-n-propylenediammonium dichloride, N,N'-tetramethylethylenediammonium dichlori e, N,N dimethy rie hylene iammonium dichloride, N,N-diethyltriethylenediammonium dichloride, N-methyl-N-ethyltriethylenediammonium dichloride, N-methyl-N-isopropyltriethylenediammonium dichloride and N,N'-dimethyldiethylenepropylenediammonium dichloride (i.e.

Many of these triethylenediamine derivatives are described and their preparation given in S.N. 799,115 filed March 13, 1959 in the names of T. E. Deger and H. Q. Smith, and now Patent No. 3,063,880.

Since nitrates are frequently desired because of their somewhat higher water solubility than halides, this proc ess has particular value with those high molecular weight halides used as disinfectants in aqueous solutions. Many of these compounds are described on pages 210 to 224 of the book by Schwartz, Perry and Berch, Vol. II, Interscience Publishers, 1958, and these componds are readily converted to the corresponding nitrates by the process of this invention.

In addition to using quaternary ammonium halides of the above types, alkyl amine halides which are not quaternaries may also be used in this process. These amine halides may be derived from primary, secondary or tertiary monoor polyamines, particularly the lower alkylamines (e.g., methylamine, diethylamine, n-butylamine, triethylamine, etc.). In US. Patent 2,919,541 there are listed a large number of such polyamines which have utility in certain rocket fuel formulations and the halides of these polyamines may be converted to nitrates by the process of this invention to thereby increase the energy available from these amine compounds.

Because of availability, the chloride salts of the amines and quaternary ammonium compounds will preferably be employed, although, as indicated, the fluorides and bromides may also be used since they too yield volatile by products.

The following examples will serve to further illustrate the invention:

Example 1.N,N-dimetlzyltriethylenediammonium dinitrate-reaction in glacial acetic acid A solution containing ml. of glacial acetic acid and 10 ml. of liquid N 0 is mixed with 4.2 g. of dimethyltriethylenediammonium dichloride and the slurry is stirred for one hour. The slurry is then filtered and the residue is washed with acetone. The yield is 5.2 grams of white solid identified as dimetyhltriethylenediammonium dinitrate and the product is free of chloride ion contamination. This represents a 98% yield based on the quaternary chloride used. The acetic acid filtrate is stirred with another 4.2 g. of chloride salt and 4 ml. of N 0 and another 98% yield of chloride-free nitrate salt is obtained.

When N-methyl-N'-ethyltriethylenediammonium dichloride is used in the above example instead of the dimethyltriethylenediammonium dichloride, pure dinitrate product is likewise obtained in essentially quantitative yield.

Example 2.Reacti0n in methanol A solution of 4.3 grams of dimethyltriethylenediam monium dichloride in 10 ml. of methanol is cooled in an ice bath (to avoid overheating) and 30 ml. of N 0 is slowly dd d to it. After 2 hours ether is added to the 5 solution and this causes the precipitation of a white solid which is filtered off and identified as dimethyltriethylenediammonium dinitrate free of chloride ion. The yield is 4.5 g., 85% of theoretical.

Example 3.-Reacti\n in water As in the above examples, 30 ml. of N 0 is added to 30 ml. of water containing 4.3 g. of dissolved diamethyltriethylenediammonium dichloride. After 2 hours an equivolume mixture of methanol and ether is added to the mixture until a white solid is precipitated. This white product is free of chloride ion contamination and it is identified as dimethyltriethylenediammonium dinitrate. The yield is 4.9 grams, 92% of theoretical.

Example 4.-Tetramethylammonium nitrate-Reaction in mixed solvents As in Example 3, tetramethylammonium nitrate is prepared by stirring a suspension of 2.2 g. of tetramethylammonium chloride in a mixture of 20 ml. glacial acetic acid, 20 ml. trichlorotrifluoroethane (CCl FCClF and and 5 ml. of N 0 The product is filtered cit after 2 hours. The yield is 2.5 g. of white solid which is identified as pure tetramethylammonium nitrate. This represents 95% of theoretical yield.

Instead of using tetramethylammonium chloride in the above example, N-methyl-N'-isopropyltriethylenediammonium dichloride is used with essentially the same results.

Example 5 Example 4 is repeated except that the mixed solvent system is replaced with acetonitrile. Pure tetramethylammonium nitrate is obtained in near theoretical yield.

In like manner, when dimethylformamide or dimethylsulfoxide is used pure tetramethylammonium nitrate is obtained in good yield.

Example 6 .Cyclic procedure As in the above examples, 2.1 g. of N,N'-dimethyltriethylenediammonium dichloride is mixed with a solution containing 30 ml. glacial acetic acid, 30 ml. of trichlorotrifiuoroethane and 5 cc. of N 0 After stirring for one hour, the white solid is filtered oil and a 98% yield of pure chloride-free nitrate salt is recovered. The filtrate is now made up to its original volume by adding cc. of a 75% trich1or-otrifluoroethane-25% CH COOH mixture. To it are added 2.1 g. of N,N-dimethyltriethylenediammonium dichloride and 2 ml. of N 0 The resulting slurry is stirred for one hour and when it is filtered yield another 98% yield of nitrate salt. Using this procedure, the filtrate is recycled 8 times, each time adding fresh chloride, N 0 and enough mixed solvent to bring the liquid to its original volume. It is found that a better than 90% yield of chloride-free product is obtained each time in the solvent is recycled. It is advantageous to use the chloride in the form of a powder free of lumps and to use about 1 cc. of N 0 for each gram of chloride salt.

The above cyclic procedure is repeated with N,N- dimethyldiethylenepropylenediammonium dichloride. The process proceeds in the same manner to give the dinitrate product in yields greater than 90% in each recycle operation.

Since it is obvious to the skilled art-worker that numerous variations and changes from the above examples may be made without departing from the spirit and scope of the invention, the invention is not to be construed as limited by the above examples and description.

We claim:

1. A process for the preparation of alkyl ammonium nitrates which comprises reacting dinitrogen tetroxide with an alkyl ammonium halide selected from the group of fluorides, chlorides and bromides and venting the volatile products, said reaction being conducted in an organic reaction medium comprising a polar liquid having at least partial solubility of alkyl ammonium nitrate product 6 to the extent of 0.1 part per parts of liquid reaction medium.

2. A process for the preparation of quaternary ammonium nitrates which comprises reacting dinitrogen tetroxide with a quaternary ammonium chloride obtained by quaternizing with a lower alkyl chloride, a tertiary amine selected from the group of lower alkyl amines and N,N'-lower alkyl polyalkylene diamines, said reaction being conducted in an organic reaction medium comprising a polar liquid having solubility for the quaternary ammonium nitrate product to the extent of at least 0.1 part per 100 parts of reaction medium, venting the nitrosyl chloride formed and separating halide-free nitrate product.

3. The process of claim 2 wherein the liquid medium is comprised of a saturated aliphatic acid containing 1 to 4 carbon atoms.

4. The process of claim 2 wherein the liquid medium is comprised of a liquid lower aliphatic nitrile.

5. The process of claim 2 wherein the liquid medium is comprised of a liquid N,N-di(lower alkyl) substituted amide.

6. The process of claim 2 wherein the liquid medium is a di-(lower alkyl) sulfoxide.

7. The process of claim 2 wherein the liquid medium is water.

8. The process of claim 2 wherein the liquid medium is acetic acid.

9. The process of claim 2 in which the reaction medium comprises a mixture of acetic acid and a liquid lower aliphatic halocarbon.

10. The process of claim 2 in which the reaction medium comprises a mixture of acetic acid and trichlorotrifiuoroethane.

11. The process of claim 2 wherein the quaternary ammonium chloride reactant is a N,N'-di-(1ower alkyl) substituted triethylenediammonium dichloride.

12'. The process of claim 11 wherein the triethylenediamine dichloride is N,N'-dimethyltriethylenediammonium dichloride.

13.The process of claim 11 wherein the triethylenediamine dichloride is N,N'-diethyltriethylenediammonium dichloride.

14. The process of claim 11 wherein the triethylenediamine dichloride is N-methyl-N-ethyl-triethylenediammonium dichloride.

15. The process of claim 11 wherein the triethylenediammonium dichloride is N-methyl-N'-isopropyl-triethylenediammonium dichloride.

16. The process of claim 11 wherein the triethylenediammonium dichloride is N,N-dimethyldiethylenepropylenediammonium dichloride.

17. A process for the preparation of quaternary ammonium nitrates which comprises reacting dinitrogen tetroxide with a quaternary ammonium chloride selected from the group consisting of tetra lower alkyl ammonium chlorides and N,N'-di(lower alkyl) substituted triethylene diammonium dichlorides, said reaction being conducted at ambient temperature and pressure in an organic reaction medium in which the quaternary ammonium nitrate product is soluble to the extent of at least 0.1 part per 100 parts of liquid reaction medium, venting the nitrosyl chloride formed, and separating halide-free nitrate product.

18. The process of making tetramethylammonium nitrate which comprises reacting N 0 with tetrarnethylammonium chloride, said reaction being conducted at ambient temperature and pressure in a reaction medium comprising acetic acid and trichl-orotrifluoroethane, venting the nitrospl halide formed and separating chloride-free tetramethylammonium nitrate.

19. The process of making N,N-dimethyltriethylenediammonium dinitrate which comprises reacting N 0 with N,N-dimethyltriethylenediammonium dichloride, said reaction being conducted at ambient temperature 7 8 and pressure in a reaction medium comprising acetic acid dison et a1.: J. Chem. Soc. (London), vol. of 1951, pages and trichlorotrifluoroethane, venting the nitrosyl chloride 1298-1303. formed and separating chloride-free N,N' dimethyltriethylenediammonium dinitrate. NICHOLAS S. RIZZO, Primary Examiner.

5 References Cited by the Examiner LEON ZITVER Examiner" Hieber: Chem. Zentr., vol. 121, page 68 (1950). Ad- 

1. A PROCESS FOR THE PREPARATION OF ALKYL AMMONIM NITRATES WHICH COMPRISES REACTING DINITROGEN TETROXIDE WITH AN ALKYL AMMONIUM HALIDE SELECTED FROM THE GROUP OF FLUORIDES, CHLORIDES AND BROMIDES AND VENTING THE VOLATILE PRODUCTS, SAID REACTION BEING CONDUCTED IN AN ORGANIC REACTION MEDIUM COMPRISING A POLAR LIQUID HAVING AT LEAST PARTIAL SOLUBILITYOF ALKYL AMMONIUM NITRATE PRODUCT TO THE EXTENT OF 0.1 PART PER 100 PARTS OF LIQUID REACTION MEDIUM.
 2. A PROCESS FOR THE PREPARATION OF QUATERNARY AMMONIUM NITRATES WHICH COMPRISES REACTING DINITROGEN TETROXIDE WITH A QUATERNARYAMMONIUM CHLORIDE BOTAINED BY QUATERNIZING WITH A LOER ALKYLCHLORIDE,A TERTIARY AMINE SELECTED FROM THE GROUP OF LOWER ALKYL AMINES AND N,N''-LOWER ALKYL POLYALKYLENE DIAMINES, SAID REACTION BEING CONDUCTED IN AN ORGANIC REACTION MEDIUM COMPRISING A POLAR LIQUID HAVING SOLUBILITYFOR THE QUATERNARY AMMONIUM NITRATE PRODUCT TO THE EXTENT OF AT LEAST 0.1 PART PER 100 PARTS OF REACTION MEDIUM, VENTING THE NITROSYL CHLORIDE FORMED AND SEPARATING HALIDE-FREE NITRATE PRODUCT.
 11. THE PROCESS OF CLAIM 2 WHERIN THE QQUATERNARY AMMONIUM CHLORIDE REACTANT IS A N,N''-DI-(LOWER ALKYL) SUBSTITUTED TRIETHYLENEDIAMMONIUM DICHLORIDE. 